In a wireless charging system, a wireless power transmitting device such as a device with a charging surface wirelessly transmits power to wireless power receiving device such as a portable electronic device. The portable electronic device receives the wirelessly transmitted power and uses this power to charge an internal battery or to power the device.
It may sometimes be desirable to transmit data from the wireless power receiving device to the wireless power transmitting device. So-called in-band communications schemes have been developed that allow wireless power receiving devices to communicate with wireless power transmitting devices. In a typical in-band communications scheme, a switching circuit that is coupled to the coil in the wireless power receiving device is used to modulate the load across the coil. The wireless power transmitting device will attempt to detect the modulated signal using a sensing circuit coupled to a coil in the wireless power transmitting device.
In-band communications schemes that are based on this type of load modulation may not always be reliable. Oftentimes, changing the load across the coil at the wireless power receiving device does not necessarily translate to a sufficiently detectable amplitude or phase change at the sensing circuit of the wireless power transmitting device.